Positive-working chemical-amplification photoresist composition

ABSTRACT

Disclosed is a novel positive-working chemical-amplification photoresist composition capable of giving an extremely finely patterned resist layer in the manufacturing process of semiconductor devices. The photoresist composition comprises: (A) 100 parts by weight of a copolymeric resin consisting of from 50 to 85% by moles of (a) hydroxyl group-containing styrene units, from 15 to 35% by moles of (b) styrene units and from 2 to 20% by moles of (c) acrylate or methacrylate ester units each having a solubility-reducing group capable of being eliminated in the presence of an acid; and (B) from 1 to 20 parts by weight of a radiation-sensitive acid-generating agent which is an onium salt containing a fluoroalkyl sulfonate ion having 3 to 10 carbon atoms as the anion such as bis(4-tert-butylphenyl) iodonium nonafluorobutane sulfonate.

This is a divisional of Ser. No. 09/920,849, filed Aug. 3, 2001,abandoned, which is a continuation of Ser. No. 09/560,558, filed Apr.28, 2000, abandoned, which is a divisional of Ser. No. 09/291,116, filedApr. 14, 1999, now U.S. Pat. No. 6,387,587 B1.

BACKGROUND OF THE INVENTION

The present invention relates to a positive-workingchemical-amplification photoresist composition or, more particularly, toa positive-working chemical-amplification photoresist compositioncapable of giving a very finely patterned resist layer on a substratesurface by patterning exposure using a KrF excimer laser beam.

As a trend in the manufacturing technology of semi-conductor devices andliquid crystal display panels in recent years, extensive investigationsare now under way to establish a photolithographic patterning process ofa resist layer having a pattern resolution of as fine as 0.25 μm or evenfiner by the use of a positive-working chemical-amplificationphotoresist composition. Turning now to the problem of the light sourcefor the pattern-wise exposure of the photoresist layer to comply withthe requirement in the manufacture of semiconductor devices toaccomplish finer and finer patterning, a photolithographic patterningtechnology for obtaining a patterned resist layer of 0.15 to 0.22 μmfineness by using a KrF excimer laser beam is the current target of thedevelopment works.

With an object to comply with the above mentioned requirements, aproposal is made in Japanese Patent Kokai 7-209868 for apositive-working chemical-amplification photoresist compositioncontaining, as the film-forming resinous ingredient, a copolymeric resinconsisting of hydroxyl group-containing styrene units, styrene units andtert-butyl (meth)acrylate units in a molar ratio of 40:20:40 or33:17:50. The there proposed photoresist composition using a copolymericresin with a relatively small amount of the hydroxyl group-containingstyrene units or a relatively large amount of the tert-butyl(meth)acrylate units is not quite satisfactory when an extremely finepatterned resist layer of 0.15 to 0.22 μm fineness is formed therewithbecause the cross sectional profile of the patterned resist layer is notfully orthogonal as desired.

In recent years, on the other hand, onium salts or, in particular, thosecontaining sulfonate ions as the anion are highlighted as anacid-generating agent used in positive-working chemical-amplificationphotoresist compositions. Examples of such an onium salt as theacid-generating agent in a positive-working chemical-amplificationphotoresist composition heretofore proposed include salts formed from abis(4-tert-butylphenyl) iodonium cation and an anion selected from thegroup consisting of camphor sulfonate ions, 4-methylbenzene sulfonateions and trifluoromethane sulfonate ions as disclosed in Japanese PatentKokai 9-179302 and onium salts containing a fluoroalkyl sulfonate ionand having at least one acid-instabilized group on a phenyl group in themolecule such as 2,2,2-trifluoroethane sulfonic acid(4-tert-butoxyphenyl) diphenyl sulfonium as disclosed in Japanese PatentKokai 10-7650.

These acid-generating agents, however, are not quite satisfactory withvarious disadvantages. For example, the onium salts having a camphorsulfonate ion or 4-methylbenzene sulfonate ion as the anion have arelatively low solubility in the organic solvent for the photoresistcompositions so that the photoresist composition cannot be compoundedwith a sufficiently large amount of the onium salt not to impart thephotoresist with high photosensitivity. In addition, the stability ofthe photoresist solution containing the same cannot be high enough and,due to the large molecular size of the compound, the distance ofdiffusion of the molecules in the post-exposure baking treatment isnecessarily not so large affecting the resolution in patterning. On theother hand, the molecular size of the trifluoromethane sulfonate ions istoo small with an excessively large distance of diffusion to cause adefect in patterning such as thinning of the resist pattern.

Further, the onium salts having an acid-instabilizable group andcontaining a fluoroalkyl sulfonate ion in the molecule are defective dueto their low solubility in the organic solvent of the photoresistsolutions to limit the amount thereof in the photoresist solutionresulting in a decreased photosensitivity and low storage stability ofthe photoresist solution. In addition, the acid-instabilizable group isliable to be decomposed when the pre-exposure baking treatment or,namely, heat-drying of the photoresist layer formed by coating isperformed at 120° C. or higher eventually to lose the activity as anacid-generating agent.

Besides the above, it is known that bis(4-tert-butyl-phenyl) iodoniumnonafluorobutane sulfonate can be used as the acid-generating agent in aphotoresist composition for exposure with an ArF excimer laser beam of193 nm wavelength. It is not certain at all, however, whether or notgood results can be obtained when the above mentioned acid-generatingagent is used in a photoresist composition for exposure with a KrFexcimer laser beam because of the difference in the resinous baseingredient of the composition which is an acrylic resin or a copolymericresin of a cyclic olefin monomer and maleic anhydride in the formerphotoresist composition and a copolymeric resin of styrene, α-methylstyrene and a (meth)acrylate ester monomer in the latter photoresistcomposition.

SUMMARY OF THE INVENTION

The present invention accordingly has an object to provide a novelpositive-working chemical-amplification photo-resist composition capableof giving a patterned resist layer having an excellently orthogonalcross sectional profile with high photosensitivity and patternresolution by the pattern-wise exposure with a KrF excimer laser beam.

Thus, the positive-working chemical-amplification photoresistcomposition provided by the present invention is a uniform blend whichcomprises:

(A) 100 parts by weight of a copolymeric resin consisting of (a) from 50to 85% by moles of hydroxyl group-containing styrene units, (b) from 15to 35% by moles of styrene units and (c) from 2 to 20% by moles ofacrylate or methacrylate ester units each having a solubility-reducinggroup capable of being eliminated in the presence of an acid, the totalof the molar fractions of the monomeric units (a), (b) and (c) being100%; and

(B) from 1 to 20 parts by weight of a radiation-sensitiveacid-generating agent which is an onium salt containing a fluoroalkylsulfonate ion having 3 to 10 carbon atoms as the anion.

In particular, the above mentioned solubility-reducing group capable ofbeing eliminated in the presence of an acid forming the (meth)acrylateester units in the component (A) is selected preferably from the groupconsisting of tertiary alkyl groups, 1-alkoxyalkyl groups and acetalgroups. Further, the anion forming the onium salt as the component (B)is preferably a nonafluorobutane sulfonate ion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The base ingredient as the component (A) in the inventive photoresistcomposition is a ternary copolymeric resin consisting of three kinds ofthe monomeric units including (a) from 50 to 85% by moles of hydroxylgroup-containing styrene units, (b) from 15 to 35% by moles of styreneunits and (c) from 2 to 20% by moles of acrylate or methacrylate esterunits each having a solubility-reducing group capable of beingeliminated in the presence of an acid, the total of the molar fractionsof the monomeric units (a), (b) and (c) being 100%. In this ternarycopolymeric resin as the component (A), the first monomeric unit (a) isa unit derived from a styrene monomer having at least one hydroxyl groupin the molecule in order to impart the copolymeric resin with goodsolubility in an aqueous alkaline solution as the developer solution.Examples of such a monomeric unit include a hydroxystyrene unit andα-methyl hydroxystyrene unit.

The third monomeric unit (c) in the copolymeric resin has a carboxylgroup protected by a group capable of exhibiting a reducing effect onthe solubility of the resin in an aqueous alkaline solution while thisprotective group is eliminated from the carboxyl group by theinteraction with an acid generated from the acid-generating agent as thecomponent (B) when the photoresist layer is exposed pattern-wise toactinic rays to release a carboxylic acid increasing the solubility ofthe resin in an aqueous alkaline solution to give a patterned resistlayer in the development treatment with an aqueous alkaline developersolution.

The solubility-reducing group capable of being eliminated in thepresence of an acid in the monomeric units of the third class (c) can beany one of known protective groups either singly or as a combination oftwo kinds or more including tertiary alkyl groups such as tert-butyl andtert-pentyl groups, 1-alkoxyalkyl groups such as 1-ethoxyethyl and1-methoxypropyl groups and acetal groups such as tetrahydrofuranyl andtetrahydropyranyl groups as preferable ones.

The monomeric unit of the third class (c) is a unit introduced by thecopolymerization of a (meth)acrylate ester monomer. This monomeric unitis represented by the general formula

CH₂—CR(CO—OA),

in which R is a hydrogen atom or a methyl group and A is theacid-dissociable solubility-reducing group including tertiary alkylgroups such as tert-butyl group and tert-pentyl group, 1-alkoxyalkylgroups such as 1-ethoxyethyl group and 1-methoxypropyl group and acetalgroups such as tetrahydropyranyl group and tetrahydrofuranyl group, ofwhich tert-butyl group, 1-ethoxyethyl group and tetrahydropyranyl groupare preferred.

The monomeric unit of the third class (c) is preferably a unit derivedfrom a monomer compound selected from the group consisting of tert-butyl(meth)acrylate, 1-ethoxyethyl (meth)-acrylate and tetrahydropyranyl(meth)acrylate in respect of the high susceptibility to acid-induceddissociation to give a patterned resist layer having an excellent crosssectional profile.

The copolymeric resin as the component (A), which consists of themonomeric units of the three classes (a), (b) and (c) in a specifiedmolar proportion, is advantageous as compared with a resin havingsolubility-reducing groups introduced into a part of the monomeric unitsof a poly-hydroxystyrene resin in respect of the largersolubility-reducing effect and smaller thickness reduction of the resistlayer by a development treatment in the unexposed areas to give apatterned resist layer having a good cross sectional profile.

In the inventive photoresist composition comprising the copolymericresinous ingredient as the component (A), which can be either one or acombination of two kinds or more of copolymeric resins falling withinthe definition of the above described ternary copolymeric resins, it ispreferable that the component (A) is a combination of a firstcopolymeric resin consisting of from 62 to 68% by moles of the monomericunits of the first class (a), from 15 to 25% by moles of the monomericunits of the second class (b) and from 12 to 18% by moles of themonomeric units of the third class (c) and a second copolymeric resinconsisting of from 62 to 68% by moles of the monomeric units of thefirst class (a), from 25 to 35% by moles of the monomeric units of thesecond class (b) and from 2 to 8% by moles of the monomeric units of thethird class (c) in a weight proportion in the range from 9:1 to 5:5 or,more preferably, from 8:2 to 6:4 in respect of the superiority in thephotosensitivity, pattern resolution and orthogonality of the crosssectional profile of the patterned resist layer.

It is preferable that the copolymeric resin as the component (A) has aweight-average molecular weight in the range from 3000 to 30000 asdetermined by the gel permeation chromatographic (GPC) method by makingreference to known polystyrene resins. When the weight-average molecularweight of the component (A) is too low, the photoresist compositioncannot be fully film-forming while, when the weight-average molecularweight of the resin is too high, the resin cannot be fully soluble in anaqueous alkaline solution.

The component (B) contained in the inventive photoresist composition incombination with the above described component (A) is aradiation-sensitive acid-generating agent which is a compound capable ofreleasing an acid by decomposition under irradiation with actinic rayssuch as ultraviolet light. It is preferable that the acid-generatingagent in the inventive photoresist composition is an onium salt compoundcontaining a fluoroalkyl sulfonate ion of 3 to 10 carbon atoms as theanion.

The cation as the counter ion of the above mentioned anion of the oniumsalt compound is not particularly limitative and can be selected fromknown ones. Suitable cations include, for example, phenyl iodonium andsulfonium ions which may optionally be substituted by a lower alkylgroup such as methyl, ethyl, propyl, n-butyl and tert-butyl groups or alower alkoxy group such as methoxy and ethoxy groups.

On the other hand, the anion of the onium salt compound is a fluoroalkylsulfonate ion obtained by substituting fluorine atoms for a part or allof the hydrogen atoms in an alkyl group of 3 to 10 carbon atoms. It ispreferable that the alkyl group in the fluoroalkyl sulfonate ion has 3to 5 carbon atoms and all of the hydrogen atoms thereof are replacedwith fluorine atoms since the acid strength of the sulfonate ion as asulfonic acid is decreased as the chain length of the alkyl group isincreased and the degree of fluorination of the alkyl group isdecreased.

Examples of suitable onium salt compounds as the component (B) include:

iodonium salt compounds represented by the general formula

in which R¹ and R² are each, independently from the other, a hydrogenatom, alkyl group having 1 to 4 carbon atoms or alkoxy group having 1 or2 carbon atoms and X⁻ is a fluoroalkyl sulfonate ion of 3 to 10 carbonatoms; and sulfonium salt compounds represented by the general formula

in which R³, R⁴ and R⁵ are each, independently from the others, ahydrogen atom, alkyl group having 1 to 4 carbon atoms or alkoxy grouphaving 1 or 2 carbon atoms and X⁻ has the same meaning as defined above.

Particular examples of the onium salt compounds suitable as thecomponent (B) in the inventive photoresist composition include diphenyliodonium nonafluorobutane sulfonate, bis(4-tert-butylphenyl) iodoniumnonafluorobutane sulfonate, triphenyl sulfonium nonafluorobutanesulfonate and tri(4-methylphenyl) sulfonium nonafluorobutane sulfonate,of which bis(4-tert-butylphenyl) iodonium nonafluorobutane sulfonate isparticularly preferable although any of the above named onium saltcompounds can be used either singly or as a combination of two kinds ormore according to need.

The amount of the onium salt compound as the component (B) in theinventive photoresist composition is in the range from 1 to 20 parts byweight per 100 parts by weight of the component (A). When the amount ofthe component (B) is too small, good pattern formation can hardly beaccomplished while, when the amount of the component (B) is too large, aphotoresist composition in the form of a uniform solution cannot beobtained due to the limited solubility of the compound in an organicsolution.

While the essential ingredients in the inventive photo-resistcomposition are the above described components (A) and (B), it isoptional, if necessary with an object to improve the fidelity of theresist pattern to the photomask pattern by preventing diffusion of theacid released by pattern-wise exposure of the resist layer to actinicrays more than necessary, that the photoresist composition furthercontains a secondary or tertiary amine compound as a component (C).Examples of preferable secondary amine compounds include aliphaticsecondary amines such as diethylamine, dipropylamine, dibutylamine anddipentylamine. Examples of preferable tertiary amine compounds includealiphatic tertiary amines such as trimethylamine, triethylamine,tripropylamine, tributylamine, tripentylamine, N,N-dimethyl propylamineand N-ethyl-N-methyl butylamine, aliphatic tertiary alkanolaminecompounds such as N,N-dimethyl monoethanolamine, N,N-diethylmonoethanolamine and triethanolamine and aromatic tertiary aminecompounds such as N,N-dimethylaniline, N,N-diethyl-aniline,N-ethyl-N-methylaniline, N,N-dimethyltoluidine, N-methyl diphenylamine,N-ethyl diphenylamine and triphenylamine, of which aliphatic tertiary C₂to C₄ alkanolamine compounds such as triethanolamine are particularlypreferable although any of these amine compounds can be used eithersingly or as a combination of two kinds or more according to need.

While additional admixture of the above mentioned amine compound withthe inventive photoresist composition may eventually cause adisadvantage of a decrease in the photosensitivity of the composition,this disadvantage can be overcome, along with a beneficial effect ofimproving the pattern resolution, by the admixture of a carboxylic acidas a component (D) in combination with the component (C). Preferablecarboxylic acids suitable for this purpose include aliphatic saturatedcarboxylic acids, alicyclic carboxylic acids and aromatic carboxylicacids.

Examples of suitable aliphatic saturated carboxylic acids includebutyric, isobutyric, malonic, succinic, glutaric and adipic acids.Examples of suitable alicyclic carboxylic acids include 1,1-cyclohexanedicarboxylic acid, 1,2-cyclohexane dicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexane dicarboxylic acid and cyclohexane1,1-diacetic acid. Examples of suitable aromatic carboxylic acidsinclude aromatic monocarboxylic acids having a hydroxyl or nitro-groupas a substituent group and aromatic polycarboxylic acids such as 2-, 3-and 4-hydroxy benzoic acids, 2-hydroxy-3-nitro benzoic acid, phthalicacid, terephthalic acid and isophthalic acid. These carboxylic acids canbe used either singly or as a combination of two kinds or more accordingto need, although the aromatic carboxylic acids are preferable due tothe adequate acid strength thereof and 2-hydroxy benzoic acid is morepreferable because this compound has high solubility in the organicsolvent for the photoresist composition and a patterned resist layer ofhigh quality can be formed on substrates of various materials from thephotoresist composition containing this acid.

As to the amount of the optional component (C) in the inventivephotoresist composition, the amine compound is added to the compositionin an amount in the range from 0.001 to 10 parts by weight or,preferably, from 0.01 to 1.0 part by weight per 100 parts by weight ofthe component (A). Addition of the component (C) in an adequate amountto the inventive photoresist composition has an effect of preventingmore than necessary diffusion of the acid generated by exposure of theresist layer to actinic rays so as to improve the fidelity of the resistpattern to the photomask pattern.

The amount of the carboxylic acid as the component (D), when added tothe inventive photoresist composition, is in the range from 0.001 to 10parts by weight or, preferably, from 0.01 to 1.0 part by weight per 100parts by weight of the component (A). Addition of the component (D) tothe inventive photoresist composition has an effect of preventing adecrease in the photosensitivity of the composition as a side effect ofthe component (C) along with a further improvement of the patternresolution.

It is usual and advantageous that the positive-workingchemical-amplification photoresist composition of the present inventionis employed in photolithographic patterning works in the form of auniform solution prepared by dissolving the essential and optionalingredients in an organic solvent. Examples of suitable organic solventsinclude ketones such as acetone, methyl ethyl ketone, cyclohexanone,methyl isoamyl ketone and 2-heptanone, polyhydric alcohols andderivatives thereof such as ethyleneglycol, ethyleneglycol monoacetate,diethyleneglycol, diethyleneglycol monoacetate, propylene-glycol,propyleneglycol monoacetate, dipropyleneglycol and dipropyleneglycolmonoacetate as well as monomethyl, mono-ethyl, monopropyl, monobutyl andmonophenyl ethers thereof, cyclic ethers such as dioxane and esters suchas methyl-lactate, ethyl lactate, methyl acetate, ethyl acetate, butylacetate, methyl pyruvate, ethyl pyruvate, methyl methoxypropionate andethyl ethoxypropionate, which can be used either singly or as a mixtureof two kinds or more according to need.

It is of course optional that the photoresist composition of theinvention is further admixed with various kinds of known additives usedconventionally in photoresist compositions including auxiliary resins toimprove the properties of the resist layer as a film, plasticizers,stabilizers, coloring agents, surface active agents and others each in alimited amount.

The patterns of the photolithographically formed patterned resist layersin the semiconductor technology can be classified into three typesincluding (1) a line-and-space pattern which is an alternate repetitionof parallel lines and parallel spaces each having the same width as theothers, (2) a hole pattern to form a contact hole and (3) an isolatedpattern which is a repetition of lines and spaces, the spaces eachhaving a width larger than the width of each line.

It is extremely difficult in the prior art to accomplish an ultrafinelypatterned resist layer including the above mentioned three types ofpatterns (1), (2) and (3) simultaneously with fineness of 0.15 to 0.22μm so that it is becoming more and more important to develop aphotoresist composition to meet the requirements in the respectiveapplications. Under these circumstances, the present invention providesa positive-working photoresist composition capable of particularlysatisfying the requirements for patterning of a line-and-space patternand a hole pattern having fineness of 0.20 to 0.22 μm.

In practicing the photolithographic patterning work by using theinventive photoresist composition to obtain an extremely fineline-and-space pattern or hole pattern of the above mentioned fineness,it is preferable, in order to adequately control the diffusing distanceof the acid generated by exposure of the resist layer to light, that thecoating layer of the photoresist composition on a substrate surface issubjected to a pre-exposure baking treatment or drying treatment aftercoating and to a post-exposure baking treatment or baking treatmentafter pattern-wise exposure to light under the following conditions.Namely, the pre-exposure baking treatment is conducted at a temperaturein the range from 120 to 140° C. or, preferably, from 130 to 140° C. andthe post-exposure baking treatment is conducted at a temperature in therange from 110 to 130° C. with the proviso that the pre-exposure bakingtemperature is higher than the post-exposure baking temperature,desirably, by at least 10° C.

When the desired resist pattern is a hole pattern, in particular, it isadvantageous that the photoresist composition is admixed withdimethylacetamide in an amount of 0.1 to 5.0% by weight based on theamount of the component (A).

The procedure of the photolithographic patterning work by using theinventive photoresist composition is not particularly different fromconventional procedures known in the technology of photolithography. Itis advantageous that the surface of the substrate such as asemiconductor silicon wafer is subjected beforehand to a treatment withhexamethyl disilazane and the like to improve adhesion of the resistlayer to the substrate surface. The photoresist composition in the formof a solution is uniformly applied to the substrate surface on a coatingmachine such as a spinner followed by drying to form a dried photoresistlayer which is pattern-wise exposed to actinic rays such as KrF excimerlaser beams through a photomask bearing a desired pattern, for example,on a minifying projection exposure machine followed by a post-exposurebaking treatment to form a latent image of the pattern. Development ofthe latent image is performed by using an aqueous alkaline solution suchas a 1 to 10% aqueous solution of tetramethylammonium hydroxide. In thisway, an extremely fine patterned resist layer of high fidelity to thephotomask pattern can be formed on a substrate surface with a finenessof 0.20 to 0.22 μm and a cross sectional profile of good orthogonality.

In the following, the positive-working chemical-amplificationphotoresist composition of the present invention is described in moredetail by way of Examples. In the following description, the term of“parts” always refers to “parts by weight”.

EXAMPLE 1

A positive-working photoresist composition was prepared by uniformlydissolving, in 800 parts of propyleneglycol monoethyl ether acetate,

60 parts of a first copolymeric resin, referred to as the resin Ihereinafter, having a weight-average molecular weight of 10,000 andconsisting of 65% by moles of hydroxystyrene units, 20% by moles ofstyrene units and 15% by moles of tert-butyl acrylate units,

40 parts of a second copolymeric resin, referred to as the resin IIhereinafter, having a weight-average molecular weight of 10,000 andconsisting of 65% by moles of hydroxystyrene units, 30% by moles ofstyrene units and 5% by moles of tert-butyl acrylate units,

3 parts of bis(4-tert-butylphenyl) iodonium nonafluorobutane sulfonate,

0.5 part of triethanolamine, and

0.5 part of salicylic acid,

followed by filtration of the solution through a membrane filter of 0.2μm pore diameter.

A semiconductor silicon wafer of 6 inches diameter after a treatmentwith hexamethyl disilazane was coated on a spinner with the aboveprepared photoresist solution followed by drying under heating on a hotplate at 130° C. for 90 seconds to give a dried photoresist layer havinga thickness of 0.7 μm. In the next place, the photoresist layer wasexposed pattern-wise to a KrF excimer laser beam on a minifyingprojection exposure machine (Model FPA-3000EX3, manufactured by CanonCo.) followed by a post-exposure baking treatment at 120° C. for 90seconds and then by a puddle development treatment at 23° C. for 65seconds in a 2.38% by weight aqueous solution of tetramethylammoniumhydroxide to give a positively patterned resist layer.

A fully resolved line-and-space pattern of 0.22 μm line width could beobtained in this way. The thus patterned resist lines had an excellentlyorthogonal cross sectional profile standing upright on the substratesurface. The minimum exposure dose for obtaining the line-and-spaceresist pattern of 0.22 μm width was 30 mJ/cm² as a measure of thephotosensitivity. The critical pattern resolution was 0.19 μm.

COMPARATIVE EXAMPLE 1

The experimental procedure was substantially the same as in Example 1excepting for modification of the formulation of the photoresistcomposition by replacing the combination of 60 parts of the resin I and40 parts of the resin II with 100 parts of a third copolymeric resinhaving a weight-average molecular weight of 10,000 and consisting of 55%by moles of hydroxystyrene units, 20% by moles of styrene units and 25%by moles of tert-butyl acrylate units.

The results of the evaluation tests of the patterned resist layer werethat line-and-space patterns of a line width smaller than 0.25 μm couldnot be obtained and the cross sectional profile of a line-patternedresist layer of 0.25 μm width was trapezoidal. The minimum exposure dosefor obtaining the line-and-space pattern of 0.25 μm line width was 30mJ/cm².

COMPARATIVE EXAMPLE 2

The experimental procedure was substantially the same as in Example 1excepting for modification of the formulation of the photoresistcomposition by replacing bis(4-tert-butyl-phenyl) iodoniumnonafluorobutane sulfonate with the same amount of triphenylsulfoniumtrifluoromethane sulfonate.

The results of the evaluation tests of the patterned resist layer werethat line-and-space patterns of a line width smaller than 0.25 μm couldnot be obtained and the cross sectional profile of a line-patternedresist layer of 0.25 μm width was trapezoidal. The minimum exposure dosefor obtaining the line-and-space pattern of 0.25 μm line width was 25mJ/cm². The critical pattern resolution was 0.24 μm.

EXAMPLE 2

The experimental procedure was substantially the same as in Example 1excepting for modification of the formulation of the photoresistcomposition by increasing the amount of the resin I from 60 parts to 80parts, decreasing the amount of the resin II from 40 parts to 20 partsand additional admixture of the composition with 2 parts ofdimethylacetamide and for an increase of the pre-exposure bakingtemperature and post-exposure baking temperature from 130° C. to 140° C.and from 120° C. to 130° C., respectively.

The results of the evaluation tests of the patterned resist layer werethat a hole pattern of 0.20 μm diameter could be obtained in this way.The thus formed hole pattern had an excellent cross sectional profileperpendicularly reaching the substrate surface. The minimum exposuredose for obtaining the hole pattern of 0.20 μm diameter was 40 mJ/cm² asa measure of the photosensitivity. The critical pattern resolution was0.19 μm.

COMPARATIVE EXAMPLE 3

The experimental procedure was substantially the same as in Example 2excepting for modification of the formulation of the photoresistcomposition by replacing the combination of 80 parts of the resin I and20 parts of the resin II with 100 parts of the third copolymeric resinas used in Comparative

EXAMPLE 1

The results of the evaluation tests of the patterned resist layer werethat hole patterns of 0.30 μm diameter or finer could not be obtainedand the sensitivity for obtaining a 0.30 μm hole pattern was 40 mJ/cm².

COMPARATIVE EXAMPLE 4

The experimental procedure was substantially the same as in Example 2excepting for modification of the formulation of the photoresistcomposition by replacing bis(4-tert-butyl-phenyl) iodoniumnonafluorobutane sulfonate with the same amount of triphenylsulfoniumtrifluoromethane sulfonate.

The results of the evaluation tests of the patterned resist layer werethat hole patterns of 0.22 μm diameter or finer could not be obtainedand the sensitivity for obtaining a 0.22 μm hole pattern, i.e. theminimum exposure dose, was 40 mJ/cm² , although the cross sectionalprofile of the hole pattern was good perpendicularly reaching thesubstrate surface.

What is claimed is:
 1. A resin composition which is a combination of tworesinous compounds comprising: a first copolymeric resin consisting offrom 62 to 68% by moles of the monomeric units (a) hydroxylgroup-containing styrene units, from 15 to 25% by moles of the monomericunits (b) styrene units and from 12 to 18% by moles of the monomericunits (c) acrylate or methacrylate ester units each having a tertiaryalkyl solubility-reducing group capable of being eliminated in thepresence of an acid and a second copolymeric resin consisting of from 62to 68% by moles of the monomeric units (a), from 25 to 35% by moles ofthe monomeric units (b) and from 2 to 8% by moles of the monomeric units(c), in a weight ratio in the range from 9:1 to 5:5.
 2. The resincomposition according to claim 1 in which the weight proportion of thefirst copolymeric resin to the second copolymeric resin is within therange of from 8:2 to 6:4.
 3. The resin composition according to claim 1wherein the tertiary alkyl group is a tert-butyl group.